Foreign matter inspection method and foreign matter inspection apparatus

ABSTRACT

In a foreign matter inspection apparatus comprising: irradiating unit for irradiating inspection light to an inspection area of an article to be inspected; intensity detecting unit for detecting intensity of either reflected light or scattered light, which is generated from the inspection area by irradiating thereto the inspection light; position detecting unit for detecting a position of either the reflected light or the scattered light within the inspection area; and deciding unit for deciding whether or not a foreign matter is present within the inspection area; the foreign matter inspection apparatus is comprised of: display unit capable of displaying thereon both a threshold image in which the threshold value is indicated over an entire area of the inspection area, and a detection sensitivity image indicated by being converted from the threshold image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a foreign matterinspecting method and a foreign matter inspection apparatus, capable ofdetecting foreign matters, scratches, defects, contaminations, and thelike (these items will be referred to as “foreign matters” hereinafter),which are present on surfaces of inspection matters such assemiconductor wafers (wafers). More specifically, the present inventionis directed to a foreign matter inspecting method and a foreign matterinspection apparatus, capable of judging whether or not the foreignmatters are present by employing threshold values.

2. Description of the Related Art

In foreign matter inspection apparatuses capable of detecting foreignmatters of semiconductor wafers, optical beams such as laser light areirradiated onto surfaces of these semiconductor wafers, and then, eitherreflected light or scattered light, which are generated from thesurfaces of the semiconductor wafers, are detected in order that foreignmatters present on the surfaces of semiconductor wafers can be detected.

In such a case where patterns which constitute respective chips havebeen formed on a surface of a semiconductor wafer, an image signal isformed from intensity of either reflected light or scattered light whichare detected; image signals of adjoining chips are compared with eachother, or the formed image signal is compared with an image signal as toa good chip which has been previously prepared; and then, when adifference between these image signals is larger than, or equal to athreshold value, it is normally so decided that the detected chip has aforeign matter.

The threshold value is calculated in such a manner that images of all ofchips which are arranged along an X-coordinate direction and aredetected by a sensor are overlapped with each other, and then, thethreshold value is calculated from variations (standard deviation) ofimages at the substantially same positions within the chips. As aconsequence, a judgement is made whether or not a foreign matter ispresent based upon a lower threshold value at a small variation, andbased upon a higher threshold value at a large variation.

An adjustment of the threshold values is related to a yield of products.The yield aspect is described in, for instance, JP-A-2001-160572 andJP-A-9-74056.

Also, a foreign matter inspection apparatus for detecting a foreignmatter of a wafer contains a foreign matter detecting system, and asurface detecting system. In the foreign matter detecting system, whilean optical beam such as laser light is irradiated onto a surface of asemiconductor wafer, either reflected light or scattered light, whichare generated from the surface of the semiconductor wafer, are detected,so that foreign matters present on the surfaces of semiconductor waferscan be detected. The surface detecting system keeps a distance of thewafer surface with respect to the foreign matter detecting systemconstant.

Conventionally, a distance between an objective lens of a foreign matterdetecting system and a surface of a wafer has been assembled andadjusted in such a manner that this distance may becomes a focaldistance based upon a designing specification of this objective lens.

Then, while this adjusted condition is continuously maintained under thesame condition even in such a case where sorts of wafers to be inspectedare different from each other, and manufacturing process steps ofsemiconductor devices are changed, the inspections have been carriedout.

However, as to focal point positions of foreign matter detectingsystems, these focal point positions of the foreign matter detectingsystems are different from each other depending upon sorts of wafers tobe inspected and manufacturing process steps of semiconductor devices.As a consequence, the conventional foreign matter inspection apparatuseshave such problems that the detection performance owned by the foreignmatter detecting systems cannot be sufficiently reflected, but thedetection performance is different from each other, depending to thesorts of wafers and the steps.

SUMMARY OF THE INVENTION

In a foreign matter inspection, as an inspecting system, image signalsare formed from intensity of reflected light, or intensity of scatteredlight which are detected; image signals of adjoining chips are comparedwith each other, or the formed image signal is compared with an imagesignal as to a good chip which has been previously prepared; and then,when a difference between these image signals is larger than, or equalto a threshold value, it is so decided that the detected chip has aforeign matter.

In the case of this inspecting system, a threshold value is calculatedin such a manner that images of all of chips which are arranged along anX-coordinate direction and are detected by a sensor are overlapped witheach other, and then, the threshold value is calculated from variations(standard deviation) of images at the substantially same positionswithin the chips. As a result, detection sensitivities are differentfrom each other, depending upon variation amounts.

Also, in order that yields are managed, required sensitivities arepresent with respect to each of areas within a chip. However, there aresuch problems that there is no indication as to the detectionsensitivities for each of the areas within the chip, and managementprecision is lowered as the yield management information.

The present invention has been made to solve the above-describedproblems, and therefore, has an object to provide a foreign matterdetecting method and a foreign matter detection apparatus, capable ofdisplaying detection sensitivities with respect to each of inspectionconditions and each of inspection areas. Also, another object of thepresent invention is to provide a foreign matter inspecting method and aforeign matter inspection apparatus, capable of setting a managementreference with respect to each of the inspection areas, and also capableof increasing precision of yield management.

On the other hand, both surface height positions of wafers (articles tobe inspected) which are detected by the surface height positiondetecting unit (surface detecting systems), and focal point positions ofthe foreign matter detecting systems are different from each other,depending upon sorts of wafers to be inspected and manufacturing processsteps of semiconductor devices.

As to the surface height position detected by the surface detectingsystem, depending upon sorts of wafers to be inspected and manufacturingprocess steps of semiconductor devices, the focal point position of theforeign matter detecting system is shifted along either the upperdirection or the lower direction. Since the shift amounts are differentfrom each other in accordance with the sorts of wafers and the steps,when recipes are formed, shift amounts are measured, and then, themeasured shift amounts must be set to recipe files.

A still further object of the present invention is to provide a foreignmatter inspecting method and a foreign matter inspection apparatus,capable of performing proper foreign matter inspections with respect tosorts of wafers and steps, and capable of providing such an informationsuitable for yield management without lowering foreign matter detectionperformance.

In a foreign matter inspection apparatus, according to an aspect of thepresent invention, while images of all of chips arranged along theX-coordinate direction are overlapped with each other, such a thresholdvalue which is calculated from a variation (standard deviation) ofimages at the substantially same positions within a chip is displayed asa threshold image within one-chip area. Also, from a threshold valuelevel of an area indicated in the threshold image within the one-chiparea, resolution within this area is displayed as a detectionsensitivity image.

Also, a foreign matter inspection apparatus, according to another aspectof the present invention, is featured by that while an optical beam suchas laser light is irradiated onto a surface of a semiconductor wafer,since either reflected light or scattered light is detected which aregenerated from the surface of the semiconductor wafer, a foreign matterpresent on the surface of the semiconductor wafer is detected.

In such a case that a pattern which constitutes each of chips has beenformed on a surface of a semiconductor wafer, an image signal is formedfrom intensity of either reflected light or scattered light which aredetected; images of all of the chips arrayed along the X-coordinatedirection are overlapped with each other; and then, threshold valueswhich are different from each other for every area are displayed as athreshold image within a one-chip area from variation amounts (standarddeviation values) of images located at the substantially same positionswithin the chips (threshold display unit). Also, a detection sensitivityimage within one-chip area is displayed from a level of the thresholdimages within a-chip area for every area. The management referenceinformation for each of the areas can be provided based upon thedetection sensitivity image within the one-chip area (resolution displayunit). Furthermore, such an information capable of reconsidering both ameasuring condition and a measuring manner can be provided with respectto such an area which cannot satisfy the required sensitivity based uponthe detection sensitivity image within the one-chip area (re-settinginstruction unit).

In accordance with the present invention, the detection sensitivitiescan be displayed with respect to each of the inspection conditions andeach of the inspection areas.

Also, in accordance with another feature of the present invention, themanagement reference can be set with respect to each of the inspectionareas, and the precision in the field management can be increased(management reference setting unit).

Also, in accordance with a further feature of the present invention, insuch a foreign matter inspecting method for irradiating inspection lightto an article to be inspected which includes a wafer; for receivinglight which is reflected, or scattered from the article to be inspected;and for inspecting whether or not a foreign matter present on a surfaceof the article to be inspected based upon intensity of the receivedlight; a focal point offset can be adjusted in such a manner that theintensity of the received light is emphasized with respect to such afact as to whether or not a wafer pattern formed on the article to beinspected is present, another fact as to whether or not a film ispresent, a material of the film, and a thickness of the film. As aresult, the proper foreign matter inspection can be realized.

Also, in accordance with a still further feature of the presentinvention, the focal point offset is adjusted to the surface heightposition detected by the surface height position detecting unit (surfacedetecting system) in such a manner that the intensity of the lightreceived by the intensity detecting unit is emphasized. As aconsequence, the proper foreign matter inspection can be realized.

Also, in accordance with a further feature of the present invention,since the function for calculating this offset amount is installed inthe recipe forming screen, the optimum conditions for the sorts ofwafers and the steps can be formed.

In accordance with a still further feature of the present invention,even when the sorts of wafer and the steps are different from eachother, the proper foreign matter inspection can be carried out, whilethe detection sensitivity of the foreign matter is not lowered.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for schematically showing an arrangement of aforeign matter inspection apparatus according to a first embodiment ofthe present invention.

FIG. 2 is a explanatory diagram for explaining a scanning operation ofan optical beam by the foreign matter inspection apparatus according tothe first embodiment.

FIG. 3 is a diagram for illustratively representing one example as to athreshold image of a one-chip image according to the first embodiment.

FIG. 4 is a diagram for illustratively showing one example as to adetection sensitivity image of the one-chip image according to the firstembodiment.

FIG. 5 is a diagram for illustratively indicating a foreign matterdetection upper limit value setting screen for each of areas accordingto the first embodiment.

FIG. 6 is a diagram for schematically showing an arrangement of aforeign matter inspection apparatus according to a second embodiment ofthe present invention.

FIG. 7A and FIG. 7B are diagrams for illustratively representing afocusing operation when the foreign matter inspection apparatusaccording to the second embodiment of the present invention is shippedfrom a factory.

FIG. 8A to FIG. 8C are diagrams for illustratively showing a focusoffset when a user handles a wafer equipped with a film, according tothe second embodiment of the present invention.

FIG. 9A and FIG. 9B are diagrams for illustratively showing a focusoffset when a user handles a wafer equipped with a pattern, according tothe second embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Next, a description is made of reference numerals used in the presentspecification. Reference numeral shows a semiconductor wafer; referencenumerals 2, 2 a, 2 b, 2 c, and 2 d indicate chips; reference numeral 10represents an illumination unit; reference numeral 20 denotes adetecting unit; reference numeral 30 shows an X scale; and referencenumeral 40 indicates a Y scale. Also, reference numeral 100 shows aprocessing unit; reference numeral 110 indicates an A/D converter;reference numeral 120 represents an image processing unit; referencenumeral 121 indicates an image comparison circuit; reference numeral 122shows a threshold calculation circuit; reference numeral 123 indicates athreshold storage circuit, reference numeral 130 represents a foreignmatter decision unit; reference numeral 131 shows a decision circuit;reference numerals 132 and 133 are coefficient tables; reference numeral140 shows a coordinate management unit; reference numeral 150 indicatesan inspection result storage unit; reference numeral 200 shows a stage Zcontrol unit; and also, reference numeral 300 shows an image displayunit.

A surface inspection apparatus of the present invention may be appliedto flat plane-shaped articles to be inspected such as semiconductorwafers, insulator wafers (for instance, sapphire glass wafer, quartzglass wafer etc.), or glass substrates for liquid crystal panel displaydevices. In the below-mentioned embodiments, the present invention hasbeen applied to inspections for inspecting foreign matters ofsemiconductor wafers. That is, embodiments of the present invention willnow be described with reference to accompanying drawings.

FIG. 1 is a diagram for schematically indicating an arrangement of aforeign matter inspection apparatus according to a first embodiment ofthe present invention.

The foreign matter inspection apparatus of the first embodiment isarranged by containing an illumination unit 10, a detecting unit 20(intensity detecting, unit), an X scale 30, a Y scale 40, and aprocessing unit 100.

The illumination unit 10 generates a laser light beam having apredetermined wavelength as inspection light, and irradiates thisoptical laser beam onto a surface of the semiconductor wafer 1corresponding to an article to be inspected along an oblique direction.

The semiconductor wafer 1 where a chip 2 has been formed on a surfacethereof has been mounted on a wafer table (not shown). Since the wafertable is moved along an X direction and a Y direction, the optical laserbeam irradiated from the illumination unit 10 is scanned over thesurface of the semiconductor wafer 1.

FIG. 2 is an explanatory diagram for explaining scanning operations asto the optical beam of the foreign matter inspection apparatus.

When the wafer table on which the semiconductor wafer 1 is mounted istransported along the Y direction, the optical laser beam irradiatedfrom the illumination unit 10 is moved over surfaces of chips 2 a, 2 b,2 c, and 2 d formed on the semiconductor wafer 1 along a directionindicated by an arrow “S1”, so that a scanning operation of one line iscarried out.

Next, when the wafer table is transported along the X direction, thescanning line is moved along the X direction. Then, when the wafer tableis transported in another direction of the Y direction, which isopposite to the above-described scanning direction of the Y direction,the optical beam is moved over the surfaces of the chips 2d, 2 c, 2 b,and 2 a along a direction indicated by an arrow S2, so that a scanningoperation of a next line is carried out.

Since these operations are repeatedly performed, the scanning operationsare carried out over the entire surface of the semiconductor wafer 1.

In FIG. 1, the optical beam which is irradiated onto the surface of thesemiconductor wafer 1 along the oblique direction is scattered bypatterns and foreign matters of the surface of the semiconductor wafer1, so that scattered light is generated.

The detecting unit 20 is constructed of, for instance, a collectinglens, a TDI (Time Delay and Integration) sensor, a CCD (Charge-CoupledDevice) sensor, a photomultiplier, and the like. The detecting unit 20receives the scattered light generated from the surface of thesemiconductor wafer 1, and converts intensity of the received scatteredlight into an electrical signal, and then, outputs the electrical signalto the processing unit 100 as an image signal.

The X scale 30 and the Y scale 40 are constituted by, for instance, alaser scale, and the like. The X scale 30 and the Y scale 40 detect aposition of the X direction and a position of the Y direction as to thesemiconductor wafer 1 respectively so as to output positionalinformation thereof to the processing unit 100.

The processing unit 100 is arranged by containing an A/D converter 110,an image processing unit 120, a foreign matter decision unit (decidingunit) 130, a coordinates management unit 140, and an inspection resultstorage unit 150.

The coordinates management unit 140, the Y scale 30, and the Y scale 40,and the like will be referred to as a position detecting unit.

The A/D converter 110 converts the image signal (namely, analog signal)entered from the detecting unit 20 into an image signal (namely, digitalsignal), and outputs the digital image signal.

The image processing unit 120 is arranged by employing an imagecomparison circuit 121, a threshold calculation circuit 122, and athreshold storage circuit 123.

The image comparison circuit 121 is arranged by containing, forinstance, a delay circuit and a difference detection circuit.

The delay circuit inputs thereinto an image signal derived from the A/Dconverter 110 so as to delay the inputted image signal. As a result, thedelay circuit outputs an image signal of such a chip whose optical beamirradiation has already been accomplished which was irradiated beforeone-chip to which the optical beam is presently irradiated in thescanning operation shown in FIG. 2.

The difference detection circuit inputs thereinto an image signalderived from the A/D converter 110 and an image signal derived from thedelay circuit so as to detect a difference between these image signals,and then, outputs the difference signal. As a result, the imagecomparison circuit 121 compares the image signals of the adjusting chipswith each other.

In such a case where a foreign matter is present on a surface of a chip,scattered light generated from the foreign matter appears as adifference of image signals as to adjoining chips.

It should be understood that the image comparison circuit 121 may bealternatively equipped with a memory instead of the above-describeddelay circuit, while the memory has previously stored thereinto data asto image signals of good product chips. Then, the image comparisoncircuit 121 may alternatively compare an image signal of a checked chipwith the image signal of the chip as the good product.

The threshold value calculation circuit 122 overlaps an image signalderived from the A/D converter 110 with an image signal derived from thedelay circuit every chip, and calculates a variation amount (namely,standard deviation) for each of the substantially same positions withina chip, and then, stores this calculated variation amount into thethreshold storage circuit 123.

The foreign matter decision unit 130 is arranged by containing adecision circuit 131 and coefficient tables 132 and 133. Coefficientsused to change threshold values have been stored in the coefficienttables 132 and 133 in correspondence with coordinates information.

The coefficient tables 132 and 133 enter thereinto coordinatesinformation supplied from a coordinate management unit (will beexplained later) 140 so as to output such coefficients to the decisioncircuit 131, which have been stored in correspondence with the inputtedcoordinates information.

In the decision circuit 131, both a threshold value and a differencebetween image signals of adjoining chips are entered from the imageprocessing unit 120, and also, coefficients used to change the thresholdvalues are inputted from the coefficient tables 132 and 133.

The decision circuit 131 multiplies the threshold value entered from theimage processing unit 120 by the coefficients entered from thecoefficient tables 132 and 133 so as to form decision-purpose thresholdvalues.

Then, the decision circuit 131 compares a difference of image signalswith the decision-purpose threshold values, and when the difference islarger than, or equal to the decision-purpose threshold value, thedecision circuit 131 judges that a foreign matter is present, and then,outputs the inspection result to the inspection result storage apparatus150.

Also, the decision circuit 131 outputs the information as to thethreshold value employed in the decision to the inspection resultstorage apparatus 150.

The coordinates management unit 140 detects both X coordinates and Ycoordinates of such a position on the semiconductor wafer 1, onto whichthe optical beam is presently irradiated, based upon the positionalinformation of the semiconductor wafer 1 entered from the X scale 30 andthe Y scale 40, and then, outputs the detected coordinates information.

The inspection result storage unit 150 stores thereinto the inspectionresult entered from the foreign matter decision apparatus 130 incorrespondence with the coordinates information entered from thecoordinates management unit 140.

Also, the inspection result storage unit 150 stores thereintoinformation as to the threshold value entered from the foreign matterdecision apparatus in correspondence with either the inspection resultor the coordinates information.

With employment of the above-described arrangement, a description ismade of a method for displaying a threshold image within one-chip area.

First of all, a preliminary inspection is carried out with respect toone line of the semiconductor wafer 1. At this time, the thresholdcalculation circuit 122 of the image processing unit 120 calculates athreshold value, and then, the calculated threshold value is stored inthe threshold storage circuit 123.

Subsequently, threshold data is read out from the threshold storagecircuit 123 so as to display a threshold image of one-chip image(threshold display unit).

It is possible to provide information for re-considering both themeasurement condition and the measuring manner with respect to the areawhich cannot satisfy the required sensitivity from the threshold imageof this one-chip image. Alternatively, an instruction for prompting are-setting operation may be outputted to the image display apparatus 300based upon this information (re-setting instruction unit).

FIG. 3 is a diagram for illustratively showing one example as to thethreshold image of the one-chip image.

While a conversion table is employed which has previously been formedfrom inspection conditions (for example, laser condition, inspectionmagnification etc.), this threshold image of the one-chip image isconverted into a detection sensitivity image of the one-chip image, andthen, the converted detection sensitivity image may be displayed(resolution display unit).

In the foreign matter deciding method, a difference image of adjoiningchips along the X-coordinate direction is compared with the thresholdvalue of FIG. 3, and then, if the difference image is larger than, orequal to the threshold value, then this difference image is decided asthe foreign matter.

As a consequence, at a place whose threshold level is high, a size of adetectable foreign matter becomes large. Conversely, at a place whosethreshold level is low, a size of a detectable foreign matter becomessmall. A table as to intensity of scattered light and foreign mattersizes is given to a relationship between the detectable foreign mattersizes (resolution) and the threshold values, so that the threshold levelof FIG. 3 can be converted into the detection sensitivity of FIG. 4.

It should be understood that the method for calculating the thresholdvalue is carried out as follows: That is, the images of all of the chipsarrayed along the X-coordinate direction are overlapped with each other,and then, the variation (standard deviation) of the images at thesubstantially same positions within the chip is multiplied by anarbitrary coefficient. As a result, the different threshold levels aredisplayed every area.

FIG. 4 is a diagram for illustratively representing one example as tothe detection sensitivity image of the one-chip image.

In addition, a foreign matter detection upper limit value may bealternatively set for each of the areas from the detection sensitivityimage of the one-chip image (management reference setting unit).Alternatively, it is also possible to manage whether or not each of thechips is good with respect to the foreign matter management reference(good/no good managing unit).

When such an inspection result is obtained which exceeds the set foreignmatter detection upper limit for each of the areas, an error may bealternatively displayed (good/no good display unit).

FIG. 5 is a diagram for illustratively showing one example as to aforeign matter detection upper limit value setting screen for each ofthe areas.

In this first embodiment, the area within the chips of the semiconductorwafer 1 is subdivided into two areas, but the present invention is notlimited thereto. Alternatively, an entire inspection area of asemiconductor wafer may be subdivided into three, or more areas inresponse to sorts and statuses of chips formed therein.

The display screens such as the threshold image, the detectionsensitivity image, and the foreign matter detection upper limit valuesetting screen as indicated in FIG. 3, FIG. 4, FIG. 5 are displayed onsuch a display unit as the image display unit 300 which is provided inthe foreign matter inspection apparatus and is shown in FIG. 6.

A description is made of a second embodiment of the present inventionwith reference to accompanying drawings.

FIG. 6 is a diagram for schematically indicating an arrangement of aforeign matter inspection apparatus according to a second embodiment ofthe present invention.

The foreign matter inspection apparatus of this second embodiment isarranged by containing an illumination unit 10 of a foreign matterdetecting system; a detecting unit 20 of the foreign matter detectingsystem; an X scale 30, a Y scale 40; an illumination unit 50 of asurface height position detecting system; a detector 60 (one set of 2detectors 60 a and 60 b) of the surface height position detectingsystem; a processing unit 100; a control unit 200 of a stage Z; and animage display apparatus 300.

The illumination unit 10 generates a laser light beam having apredetermined wavelength as inspection light, and irradiates thisoptical laser beam onto a surface of a semiconductor wafer 1corresponding to an article to be inspected along an oblique direction.

The semiconductor wafer 1 where a chip 2 has been formed on a surfacethereof has been mounted on a wafer table, namely a stage Z (not shown).Since the stage Z is moved along an X direction and a Y direction, theoptical laser beam irradiated from the illumination unit 10 is scannedover the surface of the semiconductor wafer 1.

A scanning operation of the optical beam by the foreign matterinspection apparatus according to the second embodiment is similar tothe above-described scanning operation explained with reference to FIG.2. That is, when the stage Z on which the semiconductor wafer 1 ismounted is transported along the Y direction, the optical laser beamirradiated from the illumination unit 10 is moved over surfaces of chips2 a, 2 b, 2 c, and 2 d formed on the semiconductor wafer 1 along adirection indicated by an arrow “S1”, so that a scanning operation ofone line is carried out.

Next, when the stage Z is transported along the X direction, thescanning line is moved along the X direction. Then, when the stage Z istransported in another direction of the Y direction, which is oppositeto the above-described scanning direction of the Y direction, theoptical beam is moved over the surfaces of the chips 2 d, 2 c, 2 b, and2 a along a direction indicated by an arrow S2, so that a scanningoperation of a next line is carried out. Since these operations arerepeatedly performed, the scanning operations are carried out over theentire surface of the semiconductor wafer 1.

In other words, since the stage Z is transported along the horizontaldirection of the longitudinal and lateral directions, the inspectionlight can be scanned over the entire surface of the semiconductor wafer1.

In FIG. 6, the optical beam which is irradiated onto the surface of thesemiconductor wafer 1 along the oblique direction is scattered bypatterns and foreign matters of the surface of the semiconductor wafer1, so that scattered light is generated.

The detecting unit 20 is constructed of, for instance, a collectinglens, a TDI (Time Delay and Integration) sensor, a CCD (Charge-CoupledDevice) sensor, a photomultiplier, and the like. The detecting unit 20receives the scattered light generated from the surface of thesemiconductor wafer 1, and converts intensity of the received scatteredlight into an electrical signal, and then, outputs the electrical signalto the processing unit 100 as an image signal.

The X scale 30 and the Y scale 40 are constituted by, for instance, alaser scale, and the like. The X scale 30 and the Y scale 40 detect aposition of the X direction and a position of the Y direction as to thesemiconductor wafer 1 respectively so as to output positionalinformation thereof to the processing unit 100.

The processing unit 100 is arranged by containing an A/D converter 110,an image processing unit 120, a foreign matter decision unit 130, acoordinates management unit 140, and an inspection result storage unit150.

The A/D converter 110 converts the image signal (namely, analog signal)entered from the detecting unit 20 into an image signal (namely, digitalsignal), and outputs the digital image signal.

The image processing unit 120 is arranged by containing, for instance, adelay circuit and a difference detection circuit. The delay circuitinputs thereinto an image signal derived from the A/D converter 110 soas to delay the inputted image signal. As a result, the delay circuitoutputs an image signal of such a chip whose optical beam irradiationhas already been accomplished which was irradiated before one-chip towhich the optical beam is presently irradiated in the scanning operationof the inspection light.

The difference detection circuit inputs thereinto an image signalderived from the A/D converter 110 and an image signal derived from thedelay circuit so as to detect a difference between these image signals,and then, outputs the difference signal. As a result, the imageprocessing unit 120 compares the image signals of the adjusting chipswith each other.

In such a case where a foreign matter is present on a surface of a chip,scattered light generated from the foreign matter appears as adifference of image signals as to adjoining chips.

It should be understood that the image processing unit 120 may bealternatively equipped with a memory instead of the above-describeddelay circuit, while the memory has previously stored thereinto data asto image signals of good product chips. Then, the image comparisoncircuit 121 may alternatively compare an image signal of a checked chipwith the image signal of the chip as the good product.

The foreign matter decision unit 130 is arranged by containing adecision circuit 131 and coefficient tables 132 and 133. Coefficientsused to change threshold values have been stored in the coefficienttables 132 and 133 in correspondence with coordinates information.

The coefficient tables 132 and 133 enter thereinto coordinatesinformation supplied from a coordinate management unit (will beexplained later) 140 so as to output such coefficients to the decisioncircuit 131, which have been stored in correspondence with the inputtedcoordinates information.

In the decision circuit 131, both a threshold value and a differencebetween image signals of adjoining chips are entered from the imageprocessing unit 120, and also, coefficients used to change the thresholdvalues are inputted from the coefficient tables 132 and 133.

The decision circuit 131 multiplies a predetermined value by thecoefficients entered from the coefficient tables 132 and 133 so as toform threshold values.

Then, the decision circuit 131 compares a difference of image signalswith the threshold values, and when the difference is larger than, orequal to the threshold value, the decision circuit 131 judges that aforeign matter is present, and then, outputs the inspection result tothe inspection result storage apparatus 150.

Also, the decision circuit 131 outputs the information as to thethreshold value employed in the decision to the inspection resultstorage apparatus 150.

The coordinates management unit 140 detects both X coordinates and Ycoordinates of such a position on the semiconductor wafer 1, onto whichthe optical beam is presently irradiated, based upon the positionalinformation of the semiconductor wafer 1 entered from the X scale 30 andthe Y scale 40, and then, outputs the detected coordinates information.

The inspection result storage unit 150 stores thereinto the inspectionresult entered from the foreign matter decision apparatus 130 incorrespondence with the coordinates information entered from thecoordinates management unit 140.

Also, the inspection result storage unit 150 stores thereintoinformation as to the threshold value entered from the foreign matterdecision apparatus 130 in correspondence with either the inspectionresult or the coordinates information.

The illumination unit 10 of the foreign matter detecting system isreferred to as an irradiating unit for irradiating inspection light toan article to be inspected.

The detecting unit 20 of the foreign matter detecting system is referredto as a light intensity detecting unit for receiving light which isreflected, or scattered from the surface of the article to be inspectedso as to detect intensity of light.

The illumination apparatus 50 of the surface height position detectingsystem is referred to as a surface height position detection irradiatingunit for irradiating detection light for detecting a surface heightposition onto the article to be inspected.

The detector 60 (one set of two detectors 60 a and 60 b) of the surfaceheight position detecting system is referred to as a surface heightposition detecting unit for detecting a surface height position of thearticle to be inspected. The surface height position detecting unitcontains two detectors, the detecting center positions of which aredifferent from each other along upper and lower directions of thearticle to be inspected.

The foreign matter decision unit 130 is referred to as a foreign matterdeciding unit for inspecting, or deciding whether or not a foreignmatter is present on the surface of the article to be inspected basedupon light intensity data detected by the light intensity detectingunit.

The control unit 200 controls an upper/lower position varying unit forvarying upper/lower positions of the article to be inspected by movingthe stage Z along the upper/lower directions.

A description is made of such a case that a threshold value is partiallychanged in an entire inspection area of the semiconductor wafer 1.

First of all, a preliminary inspection is carried out with respect tothe entire surface of the semiconductor wafer 1. At this time, assumingnow that all of the coefficient values stored in the coefficient tables132 and 133 of the foreign matter decision unit 130 are selected to be1, the deciding circuit 131 performs a deciding operation by employing aconstant threshold value. This preliminary inspection may bealternatively carried out with respect to either one sample or severalsamples. Also, the preliminary inspection may be alternatively carriedout for each of the inspections, or in a predetermined interval.

A description is made of a focusing point of the foreign matterdetecting system.

a function capable of detecting either reflected light or scatteredlight, which are generated from the surface of the semiconductor wafer1, is assumed as the foreign matter detecting system. This foreignmatter detecting system has such an arrangement which contains anilluminating unit 10 and a detecting unit 20 such as a lens forcollecting either the reflected light or the scattered light. A focalpoint is made coincident with an optimum surface position of thesemiconductor wafer 1 in order to detect a foreign matter. For instance,a surface position of a semiconductor wafer is made coincident with thefocal position of the detecting lens. This position is defined as thefocal position of the foreign matter detecting system.

A description is made of a focusing position of the surface detecting(surface height position detecting) system.

The beam illumination of the illumination unit 50 of the surface heightposition detecting system is entered from an oblique direction withrespect to the surface of the semiconductor wafer 1, and then, a beamwhich is reflected on the surface of the semiconductor wafer 1 in aspecular reflecting manner is detected by two sets of the photoelectricconverting elements 60 a and 60 b so as to obtain electrical signals.The angle of this beam illumination, the beam diameter, and thepositions of these two photoelectric converting elements 60 a and 60 bare arranged in a proper manner, so that the position of the surface ofthe semiconductor wafer 1 can be detected.

This surface height position detecting function is assumed as thesurface detecting system. When the position of the semiconductor wafer 1is changed along the height direction, detected electrical signals fromthe two photoelectric converting elements 60 a and 60 b become 2 maximumpoints. An intermediate point where both the signals have the same valueis present between two points where these two maximum signals areindicated. This intermediate point is assumed as a focused position ofthe surface detecting system. This focal point position may becalculated by the foreign matter inspection apparatus.

A description is made of a relationship between surface detectingoperations (surface height detecting operations) and foreign matterdetecting operations with reference to FIG. 7A, FIG. 7B, FIG. 8A, FIG.8B, FIG. 8C FIG. 9A, and FIG. 9B.

A description is made of an adjusting operation executed when theforeign matter inspection apparatus is shipped from a factory, asindicated in FIG. 7A, and FIG. 7B.

The adjusting operation is carried out by employing such a sample thateither a film or a pattern is not formed on the surface thereof such asa silicon wafer.

While a beam illuminating operation of the illumination unit 50indicated in FIG. 7A is carried out, the semiconductor wafer 1 istransported along the stage Z direction (upper/lower directions) inorder to acquire electrical signals detected by the two photoelectricconverting elements 60 a and 60 b.

As represented in an upper portion of FIG. 7B, two sets of detectedelectrical signals having maximum values are obtained. An intermediatepoint between an electrical signal 60 a whose height position indicatesa maximum value on the lower side, and an electrical signal 60 b whoseheight position indicates a maximum value on the upper side iscalculated as a coincident focal position.

The stage Z is transported along the upper/lower directions in orderthat a surface (namely, foreign matter monitoring point) of thesemiconductor wafer 1 is made coincident with this focal point position.As a result, since the focal point of the detecting unit 20 is madecoincident with the surface of the semiconductor wafer 1, an adjustingoperation is carried out in such a manner that light receiving intensityof the intensity detecting unit becomes maximum (strongest value).

As previously described, when the foreign matter inspection apparatus isshipped from the factory, the focal point offset adjustment to thefocused focal point position is carried out in such a way that the lightreceiving intensity of the intensity detecting unit is emphasized. As aresult, a proper foreign matter inspection can be carried out.

A user performs a foreign matter inspection for also a wafer equippedwith a film and a wafer equipped with a pattern.

First of all, a description is made of an adjusting operation for awafer equipped with a film, which is executed on the side of the userand is illustrated in FIG. 8A, FIG. 8B, and FIG. 8C.

In a foreign matter inspection of a wafer 1 equipped with a film shownin FIG. 8A to FIG. 8C, there are many possibilities that the foreignmatter inspections are carried out by involving a surface of the film,and a surface of the wafer 1 which is located under side of the film.

In the foreign matter inspection of the wafer 1 equipped with the film,a focal point position detected by the surface detecting system islocated at a portion “A” (namely, surface of film) shown in FIG. 8C. Inthe foreign matter inspection of the wafer 1 equipped with the film, afocal point must be focused on a position of a portion “B”. To this end,the wafer 1 is slightly moved along the upper direction. Since thisfocal point offset adjusting operation is carried out, the focal pointposition is moved to the surface (namely, foreign matter monitoringpoint) on the lower side of the film, so that the focal point of theintensity detecting unit is focused, and thus, the intensity of thereceived light can be emphasized. It should also be noted that thisfocal point offset value is calculated by a focal point offsetcalculating unit (will be described later).

Next, in a foreign matter inspection of a wafer 1 equipped with apattern shown in FIG. 9A and FIG. 9B, such a focal point offsetadjusting operation is carried out by which a foreign matter monitoringpoint is transported from a calculated focal point position to apredetermined position.

As represented in FIG. 9A, in the wafer 1 equipped with the pattern, twopieces of optical beams are generated which are reflected from thepattern surface of the wafer 1 and a portion thereof where no pattern isformed in a specular reflection manner. Electrical signals of the twophotoelectric converting elements 60 a and 60 b which detect these twooptical beams are sensed under such a condition that as indicated inpeaks (electrical signals) of 60 a and 60 b and in an upper side of FIG.9B, inclined surfaces of each of the right sides are moved from a dotline position to a solid line position. In other words, summits thepeaks (electrical signals) of 60 a and 60 b are moved along the stage Zdirection, so that the calculated focal point positions are detected atpositions which re higher than the original positions.

As a consequence, the position of the wafer 1 is slightly moved alongthe lower direction from the calculated focal point position. Since thisfocal point offset adjusting operation is carried out, the surface(foreign matter monitoring point) of the wafer 1 is made coincident withthe original focal point position, so that the focal point of theintensity detecting unit is focused, and thus the intensity of thereceived light can be emphasized. It should also be noted that thisfocal point offset value is calculated by a focal point offsetcalculating unit (will be described later).

A description is made of optimization as to a focal point offset.

This optimization may have a specific merit with respect to the wafer 1equipped with the film and the wafer 1 equipped with the pattern, asexplained with reference to FIG. 8A to FIG. 8C, and FIG. 9A to FIG. 9B.

Firstly, a wafer sample is prepared which is wanted to be measured, andthen, a general measuring condition is formed in order to measure thiswafer sample. As this wafer sample, it is preferable to employ such awafer 1 equipped with a film, or a pattern, on which PSL (polystyrenelatex) has been coated so as to be detected as a foreign matter,depending upon a use field of the adjustment.

While this general measuring condition is used, a foreign matterinspection is carried out, and then, an inspection is obtained. Itshould also be noted that a focal point offset at this time is selectedto be such a value (normally, zero) when the product is shipped. Then,the foreign matter inspection result is displayed as a foreign mattermap on the image display apparatus.

One piece, or plural pieces of foreign matter inspection portions ofinterest are selected by a user operation (inspection area settingunit), and subsequently, a focal point optimization is instructed (focalpoint optimizing process instructing unit). The foreign matterinspection apparatus receives this focal point optimizing instruction,and thus, performs the below-mentioned process operation.

While the focal point offset is varied with respect to the designatedforeign matter inspection portions (position varying unit), an image isacquired (image acquiring unit). In other words, while the stage Z istransported along the upper/lower directions, intensity data of thereceived light with respect to the respective offset values are acquiredby the intensity detecting unit (stage Z is moved along X/Y directionsso as to acquire output values of foreign matter detecting sensors inplane shape). In this process operation, a plurality of foreign matterimages may be acquired, whose total number is equal to such a numberdefined by the foreign matter inspection portions X the acquisitiontimes. The portions of the foreign matter inspections are extracted fromthe foreign matter images, so that illuminance values (intensity ofreceived light) of the foreign matter inspection portions arecalculated. Then, a proper focal point offset value for the inspectionis acquired from a graph representative of the luminance values withrespect to these focal point offset values.

This proper focal point offset value may be defined as, for example, apeak position of the luminance values, or may be defined as such acalculation value which is obtained by performing a multiplication, adivision, a subtraction, or an addition of a predetermined coefficientwith respect to the value of this peak position. These calculatingprocess operations are carried out by the processing unit 100, and areobtained from a predetermined algorithm (focal offset calculationprocess unit). Also, the above-described graph is displayed on the imagedisplay apparatus 300 such as a CRT, a flat panel display, or the like(luminance value curve display unit).

As previously explained in FIG. 8A to FIG. 8C, and FIG. 9A to FIG. 9B,even in the wafer 1 equipped with the film and the wafer 1 equipped withthe pattern, such portions that the intensity of the received light bythe light intensity detecting unit becomes maximum can be selected.

In accordance with the above-described first and second embodiments, theproper inspections can be carried out with respect to the sorts ofwafers and the steps, and the information suitable for the yieldmanagement can be provided while the detecting performance is notlowered. As a result, there is a merit capable of discovering theproblem of the process.

Also, the above-described first and second embodiments have exemplifiedboth the foreign matter inspecting method and the foreign matterinspection apparatus with employment of the dark field images causedfrom the scattered light from the surfaces of the wafers. Alternatively,the present invention may be applied to both a foreign matter inspectingmethod and a foreign matter inspection apparatus with employment oflight field images caused from reflected light from the surfaces of thewafers.

Furthermore, the present invention may be applied not only to aninspection of a wafer, but also may be widely applied to various sortsof inspections as to surfaces of various sorts of objects, for example,scratches, defects, contaminations, and the like.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A foreign matter inspecting method for comparing intensity of eitherreflected light or scattered light, which is generated from aninspection area of an article to be inspected by scanning irradiation ofinspection light, with a threshold value set to each of dividedinspection areas so as to decide whether or not a foreign matter ispresent in said inspection area; wherein: both a threshold image inwhich said threshold value is indicated over an entire area of saidinspection area, and a detection sensitivity image indicated by beingconverted from said threshold image can be displayed. 2-14. (canceled)15. An inspection apparatus which inspects a substrate comprising: anirradiating unit for irradiating inspection light on an inspection areaof said substrate; a detecting unit for detecting scattered light fromsaid substrate; a first processing unit which calculates a thresholdvalue; a second processing unit which inspects a foreign matter of saidsubstrate based on said threshold value; and a first display unit whichdisplays a distribution image of said threshold value on said substrate,wherein said first processing unit calculates a standard deviation basedon said inspection area, and calculates said threshold value bymultiplying a coefficient by said standard deviation.
 16. An inspectionapparatus according to claim 15, wherein said first processing unitcalculates said standard deviation by overlapping a plurality of imagesof a plurality of inspection areas.
 17. An inspection apparatusaccording to claim 15, further comprising, a third processing unit whichmakes a detection sensitivity image of said distribution image.
 18. Aninspection apparatus according to claim 17, further comprising, a seconddisplay unit which displays said detection sensitivity image of saidthreshold value.
 19. A method for inspecting a substrate comprising: anirradiating step of irradiating an inspection light on an inspectionarea of said substrate; a detecting step of detecting light from saidsubstrate; a first processing step which calculates a threshold value; asecond processing step which inspects a foreign matter of said substratebased on said threshold value; and a first display step which displays adistribution image of said threshold value on said substrate, wherein insaid first processing step a standard deviation is calculated based onsaid inspection area, and said threshold value is calculated bymultiplying a coefficient by said standard deviation.
 20. The methodaccording to claim 19, wherein in said first processing step saidstandard deviation is calculated by overlapping a plurality of images ofa plurality of inspection areas.
 21. The method according to claim 19,further comprising, a third processing step of making a detectionsensitivity image of said distribution image.
 22. The method accordingto claim 21, further comprising, a second display step of displayingsaid detection sensitivity image of said threshold value.